The present invention relates to brake master cylinders and more particularly, to manually actuated, power boosted hydraulic brake master cylinders for use in automotive applications.
A typical automotive master cylinder is connected in a hydraulic braking system with conduits carrying brake fluid between the master cylinder and either disc brake calipers or wheel cylinders at each vehicle wheel. Selective movement of primary and secondary pistons within the master cylinder develops elevated hydraulic pressure which is transmitted to the wheel cylinders or calipers. When an associating service brake pedal is depressed, force is transferred by a push-rod to the master cylinder primary piston which moves forward. Generally, the combination of hydraulic pressure and the force of a primary piston spring moves the secondary piston forward at the same time. When the pistons have moved forward past bypass holes in the master cylinder housing, fluid is displaced until the wheel brake linings make contact. Hydraulic pressure is then increased in the high pressure chambers of the master cylinder and is transmitted to the wheel brakes causing the brakes to be applied.
When the brake pedal is released fluid is forced back through the conduits to the master cylinder. Typical master cylinders include compensating ports through which fluid flows from the reservoir into the master cylinder during rapid brake releases. At the end of a brake release excess fluid exists in the hydraulic system due to displacement and compensation of fluid. This excess fluid returns to the reservoir through the by-pass holes of the master cylinder.
The master cylinder therefore, provides the function of responding to an application of force through a brake pedal to build pressure in the hydraulic braking system. Additionally, the master cylinder controls the flow of fluid between the brake hydraulic system and the reservoir.
A typical master cylinder is generally combined with an hydraulic or vacuum operating power booster assembly. The power booster assists in increasing the amount of force applied to the master cylinder's primary piston through the push-rod upon actuation of the brake pedal. Therefore, the master cylinder is generally constructed of a rigid structural material sufficient to carry the load imposed thereon by the push-rod. In order to carry the applied forces, master cylinder bodies have generally been constructed of cast iron or cast aluminum. A plastic reservoir is generally connected to the cast body.